Waste streams with a high organic chemical oxygen demand (COD) are an ecological burden that has to be dealt with accordingly. These waste streams can be by-products of different industries such as dairy, fruit and vegetable or sugar processing industries. An example is whey that is produced by the dairy industry as a by-product resulting from cheese making. This process results in high volumes of whey (sweet or sour) that have a high COD but on the other hand cannot be easily/economically utilised otherwise, due to the low relatively low content of useful dry content, e.g. milk protein and lactose.
Depending on the process of cheese manufacture the COD value of leftover whey can range from 35,000 mg O2/L to 100,000 mg O2/L. The main contributor of the high organic load is lactose, which can represent up to 90% of the COD value. In the case of sour whey the presence of lactic acid even increases this problem. Lactose also represents about 75% of the whey dry matter and as such can be exploited by processes utilizing microorganisms. Several solutions of whey utilisation have been studied, such as bioethanol and biogas production, extraction of lactose or proteins, production of organic acids or biomass, but there is still a need of an economical way of whey utilisation.
WO 2011/140649 describes the utilization of whey by a mixed culture of lactic acid bacteria and yeast for the production of edible biomass. The process can successfully decrease the COD load of whey, but the final product has little commercial value.
Whey can be used for the cultivation of bacteria from the genus Propionibacterium sp., belonging to the order of Actinomycetales (Bergey's Manual of Systematic Bacteriology (1st Edition, 1986)). Propionibacterium sp. are known producers of valuable products such as organic acids (propionic and acetic acid), vitamin B12 and bifidogenic compounds. While Propionibacterium sp. can be successfully cultivated on whey they cannot lower the COD load satisfactorily as they produce organic acids which accumulate in the fermented (spent) whey and contribute significantly toward the final COD load. In the following, the terms “Propionibacterium sp.” and “propionibacterium” are used interchangably.
Co-cultures of Propionibacterium sp. and other bacteria are known to be able to decrease the COD load of the spent medium (Miyano et al., 2000), but such processes have the disadvantage of not being food grade and as such being exempt from being used inside food processing plants.
The metabolites produced by Propionibacterium sp. are known to inhibit the growth of other microorganisms, especially fungi, and their use in food-spoilage prevention is well known. U.S. Pat. No. 5,260,061 describes the application of Propionibacterium sp. metabolites for food applications to inhibit the growth of yeast. WO 2008/030089 describes co-cultivation of Propionibacterium sp. with yeast for the purpose of obtaining good flavour/aroma characteristics in the cheese making process. In this case, Propionibacterium sp. was used to control and finally inhibit the growth of yeast in the mixed culture as the yeast cell applied was not tolerant to growth-inhibiting substances from Propionibacterium sp.
In view of the above stated prior art, it is an object of the invention to provide novel bioprocesses for producing valuable biotechnological products from sweet or sour whey where the final spent fermentation media exhibit a relatively low COD. Another object of the invention is to provide fungal cells useful in processes of the invention.